The present invention relates, in general, to digital mobile radio systems, and in particular, to a terminal for a digital mobile radio system and to a method for evaluating received data in a terminal for a digital mobile radio system, which offers the capability to reduce the power consumption when receiving information which is not important.
As a rule, time-division multiplexing methods are used for transmitting data in digital mobile radio systems. In this case, the bandwidth which is available on a carrier signal transmitted between base stations and mobile stations is subdivided in time between the various subscribers. Time-division multiplexing and frequency-division multiplexing methods are frequently combined in such a manner that there are a number of carrier frequencies, which are then each accessed separately using the time-division multiplexing method. Thus, for example, in the GSM system (Global System for Mobile Communications), carrier frequencies with a spacing of 200 kHz from one another are used, which are subdivided into eight time slots or data packets. In this case, data is frequently transmitted to the mobile stations from the base stations which is important for only a single one of the mobile stations, or for none of them. However, conversely, this can also relate to data packets which are sent from a mobile station to a base station. Data packets which are not important may in this case be data packets which contain so-called dummy data or filling data, but they may also be data packets which contain information that does not relate, or no longer relates, to the received terminal since, for example, the terminal has already received it once. In the prior art, all of the transmitted data is received by the receiving terminal and is processed irrespective of whether the data is or is not required by the terminal. This results in increased power consumption in the terminal which is disadvantageous, particularly for mobile stations powered by batteries such as rechargeable batteries.
Published international patent application, WO 96/37051 discloses a method and an apparatus for saving power in portable battery-powered radio appliances. In this case, a received message is compared with a previous received message. If the two messages match, the radio appliance is switched to a power saving mode, in which the message received later is not processed any further. Published international patent application, WO 94/08432 discloses a method for transmitting information between a base station and a mobile station in a digital control channel of a telecommunications system. In this case, the base station transmits change characters which indicate whether successive messages differ. The mobile station processes received messages only if a previous change character indicates a change in comparison to the previous messages. Published international patent application, Wo 94/27377 discloses a mobile station for a mobile radio system, having a receiving device for receiving digital data packets and for providing soft decision values for received data packets, and having a decision device which, before complete reception of an information unit comprising one or more data packets, uses a part of the information unit which has already been received to decide whether the information unit is or is not important and, if the decision is that the information unit is not important, causes the receiving device to ignore the rest of the information unit. In this case, the soft-decision values are used to determine whether a received data packet is or is not free of errors. If the data packet is free of errors, a power saving signal is produced.
The received data packet is furthermore compared with expected or predetermined data in order to determine whether the data packet contains information which is or is not important for the mobile station. If the information is not important, the mobile station is switched to a power saving mode, in which the rest of the received data packets are not processed any further.
It is accordingly an object of the invention to provide a terminal for a digital mobile radio system, which overcomes the hereinafore-mentioned disadvantageous of the prior art and which, specifically provides a simpler and more efficient option for saving power.
With the foregoing and other objects in view there is provided, in accordance with the invention, a terminal for a mobile digital radio system, that includes a receiver and a decision device. The receiver is for receiving an information unit including one or more data packets, where at least one of the one or more data packets including soft-decision values. The receiver is programmed to initially receive only a portion of the information unit. The decision device is programmed to use the soft-decision values to calculate a probability value indicative of whether it is important to receive an additional portion of the information unit, programmed to determine whether it is important to receive the additional portion of the information unit by comparing the probability value with a predetermined threshold, and programmed to provide a signal such that the receiver does not receive the additional portion of the information unit if it is determined that it is not important to receive the additional portion of the information unit.
The terminal does not wait until an information unit has been received completely, but an evaluation is carried out at an early stage on the basis of an already received part of an information unit to determine whether the transmitted information unit is or is not important for the relevant terminal. If the information unit is not important for the relevant terminal, then reception of the rest of the information unit is terminated. The rest of an information unit which has been identified as not being important thus may not be received or subsequently processed, and this results in a considerable reduction of the power consumption in the terminal. The terminal may be in a base station or a mobile station. Particularly in the case of a mobile station powered by batteries or rechargeable batteries, the reduced power consumption enabled by the invention provides an important advantage. Furthermore, the present invention is independent of the system in which the data is transmitted. For example, the present invention is just as applicable to the GSM system as to the DECT system (Digital European Cordless Telephone), with the time-division multiplexing method being used to transmit digital data in both systems. In the time-division multiplexing method, the data is transmitted in so-called time slots, which each contain one data packet. In the GSM system, each time frame contains eight time slots or data packets, while in the DECT system, twelve time slots or data packets are in each case provided for transmission and reception per frame.
The present invention enables information units including one or more data packets to be ignored after reception of only a part of the information unit, if the information unit is identified as not being important. In this case, a decision can be made after receiving just one data packet or a part of a data packet as to whether the associated information unit is or is not important.
For example, a signaling channel, or, in other words, an information unit containing signaling data, is provided in the GSM system, which is transmitted to the mobile stations from a base station several times per second. The signaling information unit is in this case distributed over four time slots. In each case one time slot is transmitted in one of four time frames which follow one another, that is to say the information unit is transmitted in blocks separated in time. Even after the first of four data packets is received, the present invention makes it possible to avoid receiving and thus processing the remaining three data packets, if the information unit is identified as not being important on the basis of the first received data packet.
In this case, for the purposes of the invention, not important means all information units which contain data which are irrelevant for the receiving terminal or are not required, or are no longer required, by it. Such data may be, for example, information units containing dummy data or filling data which are transmitted, for example, by a mobile station, whenever no call need be switched and, thus, no data need be transmitted in the signaling channel. Furthermore, information units which are not important may relate to data which has already been received by the receiving terminal, but is not required once again. Information units which are not important can be data which does not relate to the receiving terminal, but only relates to other terminals.
The decision as to whether the information unit is or is not important can, in this case, be made using a probability value which is calculated from the soft-decision values of the already received part of the information unit. Soft-decision values of a digital signal are provided by an equalizer in the receiving device of terminals and contain information about the statistical confidence of the transmitted digital value. In other words, the soft-decision value of a received digital signal indicates a probability value as to whether the digital signal has been transmitted correctly. Thus, a probability value is calculated by means of the soft-decision values of the already received part of the information unit, these values being a measure of the correctness of the received data. This probability value is used as a basis for the decision as to whether the information unit is or is not identified as not being important. If, as a result of this, there is a sufficiently high probability that the information unit is not important, the decision is made that the rest of the information unit should be ignored. The quality information relating to the already received part is thus used, so to speak, to calculate a probability that the information unit is not important.
In accordance with an another feature of the invention, the terminal is preferably operated in the GSM system. The information unit is in this case transmitted in a transmission channel for signaling data, in which case information data which are not important are filling data or signaling data which are not required, or are no longer required, in the terminal.
In accordance with an additional feature of the invention, the decision as to whether the information unit is or is not important is made by evaluating the information content of the already received part of the information unit and by comparing this information content with information screed in a memory device in the terminal. Specific parts, for example, bits of the information unit, may in each case be considered in this case, whose information content is defined and, for example, specifies the length of the information unit or the format of the information unit. This is particularly suitable in those cases in which the transmitted data is coded using a coding method in which the wanted bits, for example the signaling bits, influence only a certain, relatively tightly localized, portion, of all the coded bits transmitted. One example of this is the convolutional code used in the GSM system in which one wanted bit influences approximately eight coded bits.
In accordance with added feature of the invention, the already received part of the information unit is compared with information stored in a memory device in the terminal, in order to decide whether the information unit is or is not important. In contrast to the above-described features of the invention, no evaluation of the information content of the already received part is carried out in this case. The corresponding pact of an expected information unit which is not important can, in this case, be stored in a memory, for example. Such an information unit which is not important may comprise, for example, filling data. The filling data transmitted by a specific base station in a frame is normally always the same so that a decision can be made by comparing the already received part of the information unit with the corresponding stored part of the expected information unit which is not important. This is particularly suitable in those cases in which the transmitted data is coded using a coding method in which the wanted bits influence a very wide range of the coded bits transmitted. One example of this is the fire code used in the GSM system, in which one wanted bit influences up to 80 coded bits. This feature is, however, predicated on the expected information unit which is not important being known completely from the start, that is to say being completely specified.
In accordance with a further feature of the invention, a part of a previously received information unit is temporarily stored in a memory device in the terminal and is compared with the received part of a current information unit in order to decide whether the current information unit is or is not important. Thus, if an expected information unit or parts thereof which is not important is not known or specified accurately, a previously received information unit, or a part of it, is stored temporarily. The previously received information unit may in this case have been assessed or identified as not being important after complete reception and complete decoding in the terminal, for example, or it may have become unimportant subsequently. This may relate to repetitions of already received information units which the terminal no longer requires, for example, signaling data which has already been received and evaluated. For example, in GSM systems, base stations transmit requests to set up a connection (paging requests) more than just once, in order to ensure a higher probability of accessibility. If a mobile station has already received and evaluated such a request, then the corresponding information can be stored in the temporary memory, in order to avoid receiving the same data once again.
In accordance with a further added feature of the invention, the already received part of the information unit contains information as to whether the information unit is or is not important, and the terminal evaluates this information in order to make the appropriate decision. For example, the already received part of the information unit may contain information as to whether the information unit contains filing data or wanted data, for example signaling data. In the GSM system, the so-called stealing flags of some signaling channel other than the FACCH channel are preferably used for this purpose, which in each case make up two bits per data packet. This may be, for example, the CCCH channel (Common Control Channel). Thus, with this feature, it is possible to determine immediately after detecting the stealing flags whether the information unit is or is not important, and the receiver can be switched off even while the rest of the data packet is being transmitted.
With the foregoing and other objects in view there is provided in accordance with the invention, a method for evaluating data for reception in a terminal of a mobile digital radio system, which includes steps of: providing an information unit that includes one or more data packets; providing at least one of the one or more data packets with soft decision values; receiving a portion of the information unit; calculating, using the soft decision values, a probability value indicative of whether it is important to receive an additional portion of the information unit; and determining whether it is important to receive the additional portion of the information unit by comparing the probability value with a predetermined threshold.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for evaluating data for reception in a terminal of a mobile digital radio system, which includes steps of: providing a terminal; storing predetermined information in the terminal; providing an information unit that includes one or more data packets, and providing the information unit with an information content; receiving a portion of the information unit with the terminal and defining the portion of the information unit as a received portion of the information unit; obtaining the information content of the received portion of the information unit; and determining whether it is important to receive an additional portion of the information unit by comparing the information content of the received portion of the information unit with the predetermined information.
In accordance with a concomitant feature of the invention there is provided a method for evaluating data for reception in a terminal of a mobile digital radio system, which includes steps of: providing an information unit that includes one or more data packets, and providing the information unit with a portion having information relating to whether the information unit is important; receiving the portion of the information unit having information relating to whether the information unit is important; and determining whether it is desirable to receive an additional portion of the information unit by evaluating the received information relating to whether the information unit is important.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in terminal for digital mobile radio, and method for evaluating data received in such a terminal, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.